This invention relates to a new method for propagating plants, particularly solanaceous plants, from tissue cultures, particularly from cotyledon explants and from callus cultures, grown on an appropriate nutrient medium, preferably with a carbohydrate, i.e. sugar, carbon source, and particularly in the presence of exogenous carbon dioxide.
Propagation of plants from tissue cultures is a well known technique and is summarized, for instance, in the paper "Principles of Rapid Propagation" by T. Murashige, in the symposium "Propagation of Higher Plants Through Tissue Culture: A Bridge Between Research and Application", United States Department of Energy, Technical Information Center, 1978 (K. W. Hughes, et al., editors), and in the article "Plant Propagation Through Tissue Cultures," Annula Review of Plant Physiology, Vol. 25, pp. 135-166, also by Murashige.
Similary, the conditions for propagating plants from tissue cultures and by other means, and the factors involved, have been studied extensively through the years. The same is true for conditions of growing cell cultures. One of the factors which has been included in these studies from time to time is the effect of additional or exogenous carbon dioxide, that is, a quantity above the normal content of this substance in the atmosphere.
For instance, added carbon dioxide has been shown to be conducive to the propagation of certain plants from cuttings (Molnar, et al., Canadian Journal of Plant Science, Vol. 48, pp. 495-499, 1968) as well as the growth of roots in grapevines (Kriedemann, et al., Australian Journal of Plant Physiology, No. 3, pp. 605-618, 1976). Studies of the effect of carbon dioxide on tuberization of isolated potato stolons have also been conducted (Mingo-Castel, et al., Plant Physiology, Vol. 53, pp. 798-801, 1974).
The effect of carbon dioxide on the growth and properties of suspension cultures and other tissue cultures not intended for propagating plants has also been studied, for instance by Stuart, et al., Journal of Experimental Botany, Vol. 22, No. 70, pp. 96-106, (1971), Gathercole, et al., Physiol. Plant, Vol. 37, pp. 213-217, (1976) and Bergmann, Planta, Vol. 74, pp. 243-249 (1967).
U.S. Pat. No. 3,816,960 describes the effect of several factors, including the presence of one volume percent carbon dioxide, on the photosynthesis and rate of respiration of a callus culture. U.S. Pat. No. 4,326,034 describes a process for the preparation of a culture of higher plant cells capable of growing in the presence of light and in the absence of a carbohydrate carbon source in which the plant cells are initially cultivated in an aqueous medium in the presence of light, carbon dioxide, oxygen, and a maximum concentration of dissolved oxygen in the aqueous medium of 250 n mol per milliliter.
On the other hand, virtually no information is available on what effect, if any, the presence of exogenous carbon dioxide may have on the propagation of plants via organogenesis from tissue cultures. Such an experiment was attempted by Cornejo-Martin, et al., Zeitschrift Pflanzenphysiologie, Vol. 74, pp. 177-123 (1979). However, in those experiments, which involved rice callus cultures, it was determined that concentrations of carbon dioxide ranging from 1% to 20% had no effect on shoot regeneration.
According to the present invention, however, it has been found that enhanced shoot regeneration from tissue cultures of solanaceous plants, particularly those obtained by culturing explants from cotyledon tissue, and from callus, is improved by the presence of from about 0.5 to about 2.0% by volume of carbon dioxide in the culture's atmosphere.